Heart transplantation has become an established treatment for patients suffering from end-stage heart diseases. Cardiac transplant rejection is routinely determined by endomyocardial biopsy, which is not only invasive, but also prone to sampling error. A reliable non-invasive alternative for biopsy in detecting cardiac allograft rejection is desirable, but still remains as a challenge. The main goal of this research is to establish MRI-based non-invasive and sensitive indexes that not only detect acute rejection but also correctly stage rejection grades. Two-pronged approach is used in this study: First, we use MRI to detect immune cell infiltration at the rejection sites by monitoring accumulation of ultra-small superparamagnetic iron oxide (USPIO) labeled immune cells; Second, we plan to establish novel cardiac functional MRI parameters associated with cardiac dysfunction resulting from acute rejection. It has been observed that diastolic dysfunction precedes systolic dysfunction in cardiac rejection. Therefore, we will focus on developing novel hemodynamic and diastolic functional indexes with cardiac MRI. The success of this project may lead to timely and proper management of cardiac grafts and the well being of heart transplant patients.